Wheat is the main crop in most countries and forms 15 to 18% of food consumption, which used for many purposes such as bread, different pastries, starch, and protein. Drought stress is still in the production of major limitation of crops. Morphological and physiological identification of drought resistance is of highly importance in the improvement of raised problems under drought stress. As a matter of fact, the genetic relationships of each of these processes and their exact relationship with grain yield are unknown. On the other hand, the heritability of drought resistant cultivars based on morphological and physiological component modification is proposed as an important solution. This study conducted to evaluation the drought stress effect on physiological and morphological traits of wheat.

Wheat bread (Triticum aestivum L.) cultivated in a vast range of environmental situations in the whole the world and has the widest mechanism among cereal species. Land allocated for wheat production in the world is more than any other plants. Much of wheat lands planted in Iran are in arid and semiarid regions. Due to lack of water resources and drought yield environment of wheat decreases significantly in these regions. 2015-16 wheat cultivation area is 2% decreased from 9199 thousand hectares to 9180 thousand hectares. Identification of factors influencing the reduction of grain yield is difficult in harsh environments.

Basic concepts:

What is stress:

Stress in the result of the abnormal physiological processes and can be obtained by the impact or influence of biological and environmental factors. Namely stress is exposure the organism under the influence of an environment factor and apparently makes a reduction in its output or value

What is drought:

Temporary climatic conditions in which unavailability of require water for crop productivity.

Morphology:

Study of form or shape.

Physiology

Study of functions of living organisms and their parts.

Drought stress:

Low rainfall and its irregular distribution causes drought stress during crop growth period Drought and the stress resulted by it is the most important and the most common environmental stress, which causes enormous damage to crops worldwide every year, especially in Iran as an arid and semiarid country. Drought stress has severe effects on the growth of three important stages. These steps are:

Occurrence and formation of flower

Pollination and fertilization

Seed formation

In reproductive stage, the plant is particularly sensitive to water. There are many reasons that drought stress limitation prevents the rate of rise of flowering stem cells. Nevertheless, it has been proven that by removing the stress of cells it is formed faster than irrigated plants

Stress effect on photosynthesis respiration, materials transmission

Drought stress by reducing leaf area, pore blockage, reducing protoplasm activities and stabilization of carbon dioxide, reducing protein synthesis and chlorophyll reduces photosynthesis process. The conditions of severe respiratory stress, absorption of carbon, assimilate translocation, and transmission of raw materials in a wooden vessel, will rapidly decrease to a very low level, and while hydrolytic activity of the enzyme increases, reduction of assimilates saturates the levels from these substances and finally will lead to the photosynthesis reduction and hunger will happen. In terms of deficit, reduction in dry matter may be due to cell swelling pressure resulted from a reduction in the plant’s leaf area and a reduction in photosynthesis rate may be due area and a reduction in photosynthesis rate may be due to biochemical limitations resulting from water deficiency including reduction of photosynthetic pigments especially chlorophyll

Wheat production declined due to

Water supply limited during initial stage

Prolonged winter period

During the April-May unexpected rainfall (GOP, 2015-16).

In arid and semi-arid regions, salinity and water shortage are the major reasons cultivation and yield.

Due to insufficient water supply drought is also causes problem in irrigated areas (Mirbahar et al., 2009).

Effects of drought on morphological traits:

Growth more sensitive to drought stress with reverence to the grain yield.

CONCLUSION
Morpho and Physiological traits, genotypes of wheat are toughly effect during soil water scarcity. In water stress, wheat genotypes survive by adaptive variations in morphological characters and in the course of physiological and biochemical processes. Grain formation is sensitive to water shortage. Traits, such as best heading time, high RWC, rate of photosynthesis and chlorophyll contents can be use under rain fed situation, criteria of good selection for breeding of wheat genotypes.